Environmental concerns have led to a desire to ensure products are ‘biodegradable’. Many commonly used plastics show little or no biodegradability. Plastics in general have a decomposition rate of 50 to 1000 years according to their base polymer, composition and geometry. One of the most critical parameters in the development of new plastics is biodegradability of plastic polymers under composting conditions. Previous research has indicated that several natural-based polymers, including polylactic acid (PLA), could be formulated for numerous industrial applications.
Polymers manufactured from poly lactic acid have been synthesized for more than 150 years. PLA can be manufactured in a variety of forms from readily biodegradable to durable with a long lifespan. Fermentation processes have allowed for increased production of much larger volumes. Typically, the intermediate, lactic acid, is manufactured through the fermentation of sugars, starches, molasses, or the like with the help of lactic acid bacteria and/or certain fungi. The structure (L- or D-lactides) is dependent upon the selection of fermentation bacteria, and accordingly to the biodegradability properties of the final the plastic. Polylactide and its copolymers range from quickly to not very biodegradable, depending on composition. Industrial compost facilities typically offer the conditions that are necessary for degradation hydrolysis at more than 58° C. PLA is quite stable under normal circumstances but decomposes readily by the action of microbes and enzymes, and is converted into lactic acid, carbon dioxide, and water.
PLA is an aliphatic polyester and, depending on crystallinity and additives, PLA plastics are characterized by high rigidity, transparency, clarity, and gloss. PLA is odor-free and exhibits considerable resistance to fats and oils. PLA's molecular weight, density (1.25 g/cm3), and impact resistance are within acceptable ranges when compared to most major petrochemical plastics. However, pure PLA's glass transition temperature is relatively low (approximately 60° C.) and it deteriorates rapidly in moist conditions. PLA softens drastically (approximately 1/100 in elastic modulus) at Glass Transition Temperature (Tg). Softening of polymers creates tackiness and thus problems in processing/mold releasability.
PLA's utility is thus limited by its high melt viscosity, weak thermal properties, low elongation properties, poor viscoelastic properties, low softening temperature and tackiness.